The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to methods of forming gate contacts and cross-coupling contacts for field-effect transistors, as well as structures for field effect-transistors that include gate contacts and cross-coupling contacts.
Contacts may provide vertical electrical connections extending to features of semiconductor devices, such as the gate electrode and source/drain regions of a field-effect transistor. Self-aligned contacts are formed in contact openings that are constrained during etching by the configuration of adjacent structures, such as sidewall spacers and gate caps associated with the gate electrodes, as opposed to being constrained by a patterned resist.
Self-aligned contacts connected with the gate electrodes of field-effect transistors may be categorized into distinct types. One type of self-aligned contact, which is only connected with a gate electrode, is electrically isolated from nearby features, such as the epitaxial semiconductor material forming the source and drain regions of the field-effect transistor. Another type of self-aligned contact cross-couples a gate electrode with the epitaxial semiconductor material forming either the source region or drain region of the field-effect transistor, and may be used, for example, to provide cross-coupling of inverters in a logic cell. When forming a self-aligned cross-coupling contact, the top surface of the gate electrode is opened by at least partial removal of a gate cap.
A self-aligned contact providing cross-coupling may be weak if the constituent conductor formed over the gate electrode is overly thin. Such over thinning may occur during polishing to planarize the conductor that is deposited to form the self-aligned cross-coupling contact. In addition, the semiconductor material forming the related source region or drain region may be exposed to the etching process that at least partially removes the dielectric cap to open the top surface of the gate electrode, which can damage the semiconductor material.
Improved methods of forming self-aligned gate contacts and cross-coupling contacts for field-effect transistors, as well as structures for field effect-transistors that include self-aligned gate contacts and cross-coupling contacts, are needed.